A power system is constructed by connecting power generation equipment and load equipment by a power transmission facility. There are power systems in various scales from a large-scale system connecting a plurality of large-scale power plants and many factories, commercial facilities and households to a small-scale system constructed within a specific facility. The power system of any scale includes an energy management system (EMS) that manages electric power supply/demand of the entire power system, and electric power supply by the power generation equipment and electric power demand by the load equipment are balanced by the EMS.
The storage battery system is connected to the power system described above, and used as a means for balancing the electric power supply/demand. It was thought before that it is difficult to store a large amount of power, however, since a storage battery of a large capacity such as a lithium-ion battery and sodium-sulfur battery is put into practical use, it is made possible to store the large amount of power. By connecting the storage battery system including such a storage battery to the power system, an operation is possible in which excess power is charged in the storage battery when supply is excessive in contrast with power demand, and power insufficiency is compensated by discharge from the storage battery when the supply is insufficient in contrast with the power demand.
One example of suitable uses of such a storage battery system is a combination with the power generation equipment utilizing natural energy such as sunlight and wind power. The power generation equipment utilizing the natural energy is being widely introduced in response to rise in awareness of energy problems or environmental problems in recent years. However, the power generation equipment utilizing the natural energy has a disadvantage that power cannot be stably supplied since generated power tends to be controlled by natural factors such as seasons and weather. The storage battery system is a system capable of making up for the disadvantage, and by combining the storage battery system with the power generation equipment utilizing the natural energy, the power can be stably supplied.
In the case of connecting the storage battery system to the power system, an operation of the storage battery system is managed by the above-described EMS. The storage battery system includes a power conditioning system (PCS) connected to a storage battery. The PCS has a function of converting AC power of the power system to DC power and charging the DC power to the storage battery and a function of converting the DC power of the storage battery to the AC power and discharging the AC power to the power system. A charge/discharge request is supplied from the EMS to the PCS and the PCS is operated according to the charge/discharge request so that power reception from the power system to the storage battery or discharge from the storage battery to the power system is achieved. Note that the charge/discharge request supplied from the EMS to the PCS is determined so as to balance the electric power supply/demand in the entire power system.
Note that the applicant recognizes a literature described below as the one associated with the present invention. In FIG. 1 of JP 2014-124063 A, one example of the storage battery system including a plurality of PCSes connected to a power system is drawn.